[mythtv-users] VIA M787 Motherboard and mythfrontend

[Thomas Kaiser]

Hi Gert

One thing I forgot in my last mail. I don't have anything connected to the PCI 
Bus. At the moment I have only the cdrom connected to the 2. IDE controller. The 
IDE-CompactFlash adapter is removed. And I tested the settings with KnoppMyth, 
but no luck. More comments "inline".

Gert van der Knokke wrote:
>> I didn't see the "Via-XVMC decoder" setting, but I will look again, thanks.
>> For what does "Via-XVMC" stands for?
>>
>>   
> It can be found in the playback settings, I'm not sure in which language 
> you have installed your Myth system (mine is in Dutch...)

I use English at the moment, but no problem to find the settings.

> 
>  From the main menu:
> 
> Configuration -> Configuration -> TV -> Playback
> 
> There is an option to select the 'preferred MPEG-2 decoder' and here you 
> can choose Standard, libmpeg2, Standard XVMC and VIA XvMC.
> You need to select the last one: VIA XvMC
> This decoder uses some hardware videoacceleration of  the Via videochip.
> For best results on a monitor you need to enable 'deinterlace playback' 
> and select Bob2x as deinterlacer.
> 
> Then keep pressing Enter (NOT ESC!!!) until you come back at the menu 
> again (otherwise none of your changes are saved)

Yes, I did it like this and the settings should be really saved. But I noticed 
one wired thing. I made the settings and did some tests. This was run from the 
KnoppMyth liveCD and I decided to reboot an power off. The KnoppMyth CD did 
start again and I went to the menu to choose the right option but the correct 
options were alredy checked!
How can the liveCD remember what I checked? I did a cold boot!?

> 
> After this you can go back with ESC until you get at the main menu 
> again, now try and play a recording or live TV, it should play much 
> smoother and CPU use should be about 40 to 60 % with a 720x576 8Mbit 
> Mpeg2 file on a 1024x768 monitor.
> 
> I run my X at 1280x720 at 50Hz on a 26" Acer LCD TV and it works OK (about 
> 65% CPU)

I am running it at 1280x1024 right know and have 100% CPU usage.

>> Actually the idea was to boot of a CF card as a HD but it seems that the CF card 
>> is much slower than a real HD :-(.
>>
>>   
> That should be no problem as the frontend hardly uses the harddisk 
> during playback of files from a seperate backend. The harddisk lights on 
> my frontends only occasionally blink. Just put in enough RAM (256 is too 
> little, 512 Mb should be enough) One of my frontends runs from a 6Gb 
> 2.5" laptop drive without problems.

I think so, as I booted from the KnoppMyth CD without the CF card.
I have 512MB RAM installed.

> 
>> I installed a basic Ubuntu and added only the packages as I needed (and a little 
>> more for xorg, I think). Anyway, It boots and runs, but I have still the same 
>> jitter problem. When I look at the kernel messages I see that DMA gets disabled. 
>> Maybe this is the problem. The CF card has no DMA :-(
>> In the mythtv log I see some "prebuffer underrun" or somthing like this, I don't 
>> have access to the log right now, sorry.
>>   
> You get the prebuffer pauses because the CPU has to do all of the 
> decoding and it can not keep up. That is why you need the Via XvMC 
> decoder option.

Even with the Via XvMC option, the CPU is running at 100% :-(

> 
>> Now, I will try to get something together which just loads form the CF card and 
>> runs in ram. I did a lot of reading about "initramfs", I think this the way to 
>> go, or not?
>>
>>   
> You could try and boot of the card, then mount a root filesystem over 
> the network and run the frontend from there.

Yes, But I just search for a easy method to test if this MB is capable for a 
Mythtv frontend. Now, It looks like it gets a really big project.
Anyway, I like the idea of loading the whole filesystem to the ramdisk and the 
whole system runs in RAM -> Speed!? :-)

> 
>> I will work on this for some time or buy some other hardware :-(
>>
>>   
> If you are planning to go HDTV then you definitely need more horsepower.
> For standard PAL/NTSC (SDTV) signals, this board will do fine and runs 
> quite cool too...

Not in a near future. I am happy if I can run PAL without jitter :-)


Thomas


-- 
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